In recent years, containers from polyalkylene terephthalates such as polyethylene terephthalate (referred to hereinbelow as “PET containers”) have been widely used as containers for beverages such as tea, coffee, black tea, milk beverages, and carbonated refreshing beverages.
Furthermore, in addition to conveyors from metallic materials such as stainless steel, conveyors from resin materials such as polyacetal resins, polypropylene resins, polyethylene resins, acrylonitrile-butadiene-styrene resins, etc. (referred to hereinbelow as “resin containers”) have been used in the processes of manufacturing and filling the beverages.
Resin conveyors are usually used for transporting PET containers in the process of filling the containers with the above-described beverages.
Resin conveyors are continuously operated under automatic control. As a result, even when the flow of PET containers is stopped, the resin conveyor alone continuous operating. In this case the dynamic friction force between the PET container and conveyor surface has to be decreased.
Further, an appropriate static friction force is required for the conveyor surface in order to place the PET containers that were supplied from a washing machine directly onto the flow of resin conveyor.
For this purpose, Japanese Patent Application Laid-open No. H1-96294 has discloses a lubricant composition comprising a higher fatty acid soap as the main component and optionally a surfactant obtained by compounding a cationic surfactants having Bactericidal ability and a nonionic surfactant. Such lubricant composition is used by diluting with water to a concentration of the higher fatty acid of about 0.01 to 0.1% and supplying onto a conveyor by appropriate method such as coating.
However, lubricating ability of such lubricants comprising the a higher fatty acid soap as the main component is sometimes affected by hard components of the water used. Thus, such lubricants react with hard components of the water used, producing scale, and this scale accumulates on the conveyor surface and decreases the lubrication thereof. Moreover, microorganisms (fungi) inevitably appear in the scale. Yet another problem is that the nozzles for supplying the lubricant are clogged with the scale. Accordingly, Japanese Patent Application Laid-open No. H2-97592 discloses a bactericidal lubricant for transferring bottles and cans, the lubricant comprising a specific anionic surfactant and a bactericidal quaternary ammonium cationic surfactant.
Furthermore, if such lubricants adhere to PET containers for carbonated beverages, because the inside of the container is pressurized by the carbon dioxide gas, stresses appear therein causing stress cracking of the PET container. As a result, there is an unavoidable risk that the PET container will be damaged and that the liquid beverage filling the inside of the container will leak.
Japanese Patent Application Laid-open No. H6-172773 discloses a lubricant for a bottle conveyor for PET containers for a process of filling the containers with a carbonated refreshing beverages, in which an alkyl diphenyl ether disulfonic acid salt is added to a lubricant composition comprising a water-soluble fatty acid alkali salt as the main components, whereby stress cracking of PET containers is prevented or inhibited, while lubricating ability is being maintained.
Further, as a lubricant for resin conveyors, Japanese Patent Application Laid-open No. H10-158681 discloses a lubricant for a bottle conveyor made from a synthetic resin such as polyacetal resin that comprises as the main component an aqueous solution containing 0.0025 wt. % or more of polyethylene glycol-type nonionic surfactants composed of at least one block copolymer of a polyoxyethylene alkyl ether, a polyoxyethylene fatty acid ester, or polyoxyethylene and polyoxypropylene, this lubricant having excellent washing ability and lubricating ability and causing no scale.
However, the problem associated with polyethylene glycol-type nonionic surfactants with HLB 10 to 16 is that they affect stress cracking of PET containers. Furthermore, there is a need for a compact lubricant composition that can be used with a high dilution ratio